Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F9/00—Multistage treatment of water, waste water or sewage
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/58—Treatment of water, waste water, or sewage by removing specified dissolved compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/18—Treatment of sludge; Devices therefor by thermal conditioning
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/02—Temperature
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/06—Controlling or monitoring parameters in water treatment pH
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to a process for the treatment of aqueous sulphuric acid containing dissolved metal salts.
• Impure aqueous sulphuric acid solutions containing, particularly, iron sulphates wherein the iron content is substantially wholly in the ferrous state are produced in large quantities by the steel industry (as "pickling liquor") and by the titanium dioxide industry in the operation of the so-called ⁇ sulphate ⁇ process.
• the solution also contains smaller quantities of other metal salts, normally the sulphates, derived from impurities in the starting material for the process e.g. ilmenite or an iron-containing titaniferous slag produced by the electro smelting of ilmenite.
• the salts are aluminium and magnesium sulphates.
• aqueous sulphuric acid solutions should be treated to reduce their acidity and to remove at least the greater part of the dissolved salts in the form of a solid which can be disposed of, for example as land fill and/or as a starting material or component for other processes. It is an object of the present invention to provide such a process.
• the present invention is a process for the treatment of an aqueous sulphuric acid solution of a metal salt or salts comprising the following steps:
• Adjustment of the pH in step (a) above is normally carried out to a value in the range 1 to 5.5 and particularly a value in the range 1 to 3, for example to about pH 2.
• This is preferably accomplished by the addition of calcium oxide, calcium sulphide or calcium carbonate.
• the calcium oxide or calcium sulphide may be obtained by the calcination of previously precipitated calcium sulphate which has been calcined at a temperature in the range 700° to 1350° C and particularly at a temperature in the range 1200° to 1250° C to form calcium oxide or at a temperature in the range 700° to 1150° C, particularly in the range 1000° to 1100° C to form calcium sulphide. In the latter case it is preferred that the calcined material contains less than about 5% calcium sulphate after calcination but its content of calcium oxide is not critical.
• step (a) it is not, of course, necessary that all the calcium sulphate produced in step (a) should be calcined to calcium oxide or calcium sulphide.
• Some precipitated calcium sulphate may be utilised in other processes, for example in the production of plaster or plaster board and where this is to be done it is advisable to adjust conditions to precipitate the calcium sulphate in the particular physical form which is most useful for its intended purpose.
• some of the calcium sulphate may be calcined with other compounds, for example with the appropriate silicates to produce cement. Both proceses i.e. the production of plaster, plaster board and cement are well known and have previously been described in detail.
• step (a) hydrogen sulphide is evolved and may be recovered and used as a fuel in the calcination of calcium sulphate or it may be burned with sulphur dioxide to form elemental sulphur.
• H 2 S it may be possible to recover more H 2 S from the liquor by conventional stripping techniques.
• Sulphur dioxide produced by the combustion of H 2 S for example when the latter is used as a fuel in the calcination of calcium sulphate (together with sulphur dioxide from the conversion of calcium sulphate to calcium oxide) may also be utilised in the production of sulphuric acid or it may be burned with H 2 S to form elemental sulphur.
• the precipitate is separated from the mother liquor by decantation, by the use of a centrifuge or by filtration and the calcium sulphate is treated as described above.
• this is normally achieved under reducing conditions, for example in a rotary calciner or fluidised bed heated by the combustion of a fuel.
• the reducing conditions may be provided by the products of combustion of the fuel and/or by an added reducing agent such as carbon.
• the calcium sulphate prior to calcination is usually in the form of the dihydrate CaSO 4 .2H 2 O.
• the pH of the mother liquor, after removal of the calcium sulphate (and H 2 S if necessary) is adjusted to a value in the range 7 to 9.
• This may be carried out by the addition of calcium oxide, calcium sulphide, calcium hydroxide or by the addition of the calcium-containing, calcined solids from step (d).
• the calcium oxide, hydroxide or sulphide may be obtained by the calcination of calcium sulphate from step (a) and the formation of suitable calcined, calcium-containing solids from step (d) is described later in this specification.
• the disadvantage of using calcium sulphide in the treatment of the mother liquor is that some of the metals precipitated from the mother liquor are in the form of their sulphides and/or hydroxides and these are difficult and/or unpleasant to handle and must be calcined at a relatively high temperature to give an innocuous and acceptable land fill. It is preferred, therefore, to utilise calcium oxide and/or calcium hydroxide or calcined, calcium-containing solids in step (c) since these precipitate calcium sulphate and the oxides/hydroxides (as opposed to the sulphides) of the other metals and such a mixture may require calcination only at a relatively low temperature to produce a dry handleable and acceptable solid. Calcination at a temperature in the range of about 650° to 750° C, preferably under oxidising conditions, has been found to be very suitable if the calcium sulphate content is to remain unchanged.
• step (c) The calcium sulphate which is precipitated with the sulphides, oxides and/or hydroxides in step (c) assists in providing a more readily filterable product.
• the precipitate including the calcium sulphate
• the sulphur dioxide, formed may, as before, be utilised in the production of sulphuric acid and/or in the production of sulphur.
• the final, relatively inert solid from the calcination of the precipitate from the mother liquor may be used as land fill; in cement production or it may be used, at least in part, to neutralise the mother liquor from the initial precipitation of calcium sulphate i.e. in step (c). It is, of course, preferred to utilise material which has been converted substantially completely to the corresponding metal oxides by calcination for neutralisation of the mother liquor for this purpose.
• the purpose of the present invention is to convert a strongly acidic solution of metal salts (which is extremely difficult to dispose of) into a relatively pure and innocuous liquid which can be discharged into any receiving water without difficulty and a relatively inert solid which can be used for land fill or which can be utilised as a raw material for other processes.
• a combination of all three possibilities provides a most attractive method of dealing with a difficult problem.
• the pH value of the mother liquor obtained after filtering off the calcium sulphate as described previously was adjusted to about 8 by the addition of calcium oxide derived from the previous step and the mixture was stirred. A coloured precipitate formed which was allowed to settle before recovery by filtration.
• the mixture of metal hydroxides, oxides and calcium sulphate obtained by filtration was dried, ground, mixed with coke and treated in a heated fluidised bed, as previously described. The bed temperature was maintained at 1250° C throughout by means of the hot combustion products from an oil burner.
• the product was a dry lightly-coloured inert solid consisting of metal oxides which was very suitable for handling e.g. for dumping on land.
• the mother liquor from the second adjustment of the pH value was relatively pure water and was of suitable quality for discharge into receiving waters without detrimental effect.
• aqueous sulphuric acid solution of metal salts containing sulphuric acid, iron sulphate and other metal sulphates including those of aluminium and magnesium and similar in all respects to the effluent from a sulphate process for the production of TiO 2 was taken and to this was added an aqueous slurry of calcium sulphide and calcium oxide (molar ratio 1.5:0.5) until the pH value was about 1.5.
• the mother liquor (and washings) was a relatively pure liquor suitable for discharge to any receiving waters.
• Example 2 The process described in Example 2 was repeated to the formation of the mother liquor after the precipitation of calcium sulphate at pH 1.5 and the removal of the calcium sulphate (for calcination).
• the pH value of the mother liquor (and washings) was adjusted to 8.5. by the addition of an aqueous slurry of lime with stirring.
• a light coloured precipitate was formed consisting of a mixture of calcium sulphate (as gypsum) and the hydroxides/oxides of other metals such as aluminium and magnesium which are precipitated under these conditions. It was necessary only to calcine this at about 150° C to form an easily handleable solid for disposal. Calcination at higher temperatures was unnecessary since there were no metal sulphides to decompose.
• the dried material was an innocuous, relatively inert solid suitable as land fill and the mother liquor was a relatively pure aqueous liquid at an approximately neutral pH value suitable for discharge into any receiving water.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Hydrology & Water Resources (AREA)
• Water Supply & Treatment (AREA)
• General Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Geology (AREA)
• Thermal Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Inorganic Chemistry (AREA)
• Removal Of Specific Substances (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

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Cited By (6)

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Citations (4)

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• 1974
  • 1974-10-12 GB GB4429774A patent/GB1454933A/en not_active Expired
• 1975
  • 1975-09-26 DE DE19752543005 patent/DE2543005A1/de not_active Withdrawn
  • 1975-10-02 US US05/619,002 patent/US4006080A/en not_active Expired - Lifetime
  • 1975-10-08 CA CA237,299A patent/CA1071839A/en not_active Expired
  • 1975-10-09 JP JP50122387A patent/JPS5176192A/ja active Pending
  • 1975-10-10 FR FR7531146A patent/FR2287421A1/fr active Granted
  • 1975-10-11 ES ES441720A patent/ES441720A1/es not_active Expired

Patent Citations (4)

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